Motor protector or circuit breaker and bimetal blade therefor



MOTOR PROTEOTOR OR CIRCUIT BREAKER AND BIMETAL BLADE THEREFOR Filed Feb. 14, 1955 March 25, 1958 H F MALONE 2,828,386

INVENTOR Homer F. Malone BY ATTbRNEYs United States Patent MOTOR PROTECTOR OR CIRCUIT BREAKER AND BHVIETAL BLADE THEREFOR Homer F. Malone, Millburn, N. J., assignor to The Wilcolator Company, Elizabeth, N. J., a corporation of Delaware Application February 14, 1955, Serial No. 487,749

Claims. (Cl. 200-113) My invention relates to improvements in circuit breakers or motor protectors provided with a novel snapacting bimetallic blade. More particularly, the invention relates to an improved motor protector or circuit breaker to be mounted in the electrical supply circuit of a motor to protect the motor against current overloads.

The principal object of the invention is to provide a compact relatively inexpensive circuit breaker unit consisting of a minimum number of parts which are rigidly held together and readily included in the electrical supply circuit of an electric motor.

A further object of the invention is to provide an improved temperature-responsive bimetallic blade through which electric current is adapted to flow.

Another object of the invention is to provide a circuit breaker unit which is readily adjustable for quick resetting.

According to my invention, the improved temperatureresponsive circuit breaker comprises a mounting member, a pair of electrical terminals carried by the mounting member, a fixed electrical contact electrically connected to one of said terminals, snap-acting bimetallic blade carried by the mounting member and including a body substantially circular in shape and having a cutout tongue centrally located and integrally connected at one end to the body of the blade. In this construction the bimetal blade is fixed to the mounting member by attaching the tongue of the blade thereto so that when the blade is snapped, the body portion of the blade moves away from the mounting. A contact is fixed to the body of the blade opposite the extending or free end of the tongue and the blade is oriented so that the contact carried thereon normally engages the fixed contact carried by the mounting, and means is provided for connecting the blade through the tongue to the other electrical terminal carried by the mounting.

According to a preferred construction, the bimetallic blade is substantially uniform in width around the tongue and the tongue has approximately the width of the peripheral portion of the blade. blade is preformed so that its body portion is dished or concave on its high-expanding side to present a substantially spherically-shaped formation centered with respect to the outside of the blade. This dishing is effected, however, Without changing the flat straight shape of the tongue.

The improved circuit breaker preferably and advantageously includes an adjustable stop means for restricting the extent of movement of the blade when it snaps to open the circuit, in order to materially reduce the temperature differential between the closing and opening of the circuit.

The circuit breaker or motor protector and the improved blade, according tothe present invention, include other features and advantages, described more in detail hereinafter in connection with the accompanying drawings showing one embodiment of the invention.

Furthermore, the

2,828,386 Patented Mar. 25, 1958 "ice In the drawings:

Fig. 1 is a plan view of a circuit breaker, including the improved bimetallic blade, constructed and arranged in accordance with the invention;

Fig. 2 is a longitudinal, vertical, sectional view through the circuit breaker taken on the line 2-2 of Fig. l, in which the switch of the circuit breaker is shown in closed position;

Fig. 3 is a broken vertical sectional view similar to that of Fig. 2, showing the circuit breaker in open-switch position with the body of the bimetallic blade snapped to its opposite position.

The embodiment of the circuit breaker shown in the drawing comprises a mounting 10 and a bimetallic blade 12 mounted thereon. The mounting 10 comprises a metal plate 14 having an integral electrical terminal 16 and is provided with downwardly-extending lugs 18 bent around and retaining a block or sheet of insulating material 20, which is almost entirely covered on top by the metal plate 14. The lower lugs 18 as shown in Fig. 1 are respectively on opposite sides of a projection 21 of the sheet 20 and prevent shifting of the sheet. The plate 14 also includes spaced projecting attachment brackets 22 extending downwardly along the edge of the sheet or block 20 and provided with holes for securing the circuit breaker to an instrument panel or switchbox. A fixed electrical contact 24 in the form of a contact rivet is arranged in an opening 26 in the metal plate 14, the rivet extending through the insulation 20 and a sheet metal electrical terminal 28 and being riveted over at 30 to firmly secure the terminal 28 to the underside of the sheet of insulation 20. The contact 24 is spaced from the plate 14 so that it and the terminal 28 are insulated with respect to the metal plate 14. The sheet metal terminal 28 includes a portion bent up in a notch in the insulation 20 to prevent swinging of the terminal on the rivet 24.

The bimetal blade 12 is circular in shape, except for the cut-off sides for reducing its Width, as shown in Fig. l, the blade comprising a body portion 32 having a U-shape cut-out slot 34 leaving a tongue 36 integral with the body 32. The sides of the U-shaped slot are parallel to the cut-off sides of the generally circularshaped body. The underside of the body of the bimetal blade is provided with an electrical contact 33 adjacent the free end of the tongue, and is fixed to the mounting 10 in a position such that the contact 38 engages the fixed contact 24. A rivet 40 extends centrally through the tongue 36, and centrally of the body 32, through a spacing Washer 42 and a hole in the plate 14 and is riveted-over under the plate 14 at 44 within an opening 46 in the sheet of insulating material.

The assembly held by the rivet 44) also includes a sheet metal stop 43 secured in fixed position under the head of the rivet 40 and extending out over the upper portion of the body of the bimetal blade 12 directly above the position of the contact 38.

The bimetal blade 12, except for the tongue 36 is prestressed in a press, so that it has predetermined operating characteristics. The blade is prestressed in a die having a spherically-shaped formation but which is open at the position of the tongue, so that a concave spherical shape is imparted to the body portion of the blade centrally with respect to its outside on its high-expanding side. The predetermined operating characteristics of the blade determine the degree of concavity imparted thereto. In the pressing operation the tongue is left perfectly straight and flat so that it bends freely in use. When the blade is heated up, the end portion of the tongue integral with the body of the blade is gradually elevated with respect to the mounting, thereby applying progressively a increasing pressure on the contact 24 until the blade reverses its concavity and snaps to open circuit position. When the circuit breaker or motor protector of the present invention is connected into one of the current supply leads or" an electric motor, by means of the terminals fit? and 28, current flows, for example, through the terminal 28, the contact rivet 24 to contact 38, through both sides of the body portion of the blade 12, into the tongue 36 and then through the rivet 4-0 and washer 42 to the plate 14 and terminal 16. If the current becomes excessive, the bimetallic blade is heated up by the current and snaps to the position shown in Fig. 3 and thereby breaks the circuit to the motor and protects it from any damage. The tongue 36 of the bimetal blade adjacent to the body portion 32 is heated up more rapidly than the peripheral body portions of the blade because it has a cross-sectional area and current-carrying capacity which is only about one-half that of the combined crosssectional areas of the body portions of the blade leading fromthe contact 38 to the tongue 36. The tongue, therefore, elevates the portion of the blade to which it is attached and applies increasing contact pressure more and more until, when the current is sufiicient to cause circuit rupture, the pressure on the fixed contact causes the blade to open the cir uit with a quick decisive snap action.

In many instances, it is desirable to have the blades reset, that is, returned to closed position at a temperature higher than their normal reset temperature. In other words, it may be desirable to change the temperature differential between closing and opening. For example, the blades may have a normal temperature differential of 100 F., and it may be desirable to reduce this to from 3 to 50 F. This may be accomplished by means of the stop 48, the free end of which may be bent down to limit the upward movement of the body of the blade when it snaps to open position. The reset temperature may be raised by bending the free end of the stop 48 downwardly to restrict the opening movement of the blade. When the blade is tested or calibrated, this stop can be adjusted to the desired reset temperature or time, so that the blade is prevented from opening up fully to its natural position and consequently obtain a quicker resetting, at a higher temperature. In the present instance, the stop 48 is particularly useful because of the structure and manner of mounting the bimetal blade, which causes it to snap open with a naturally wide gap. In most uses for which the circuit breaker is applied, the circuit breaker should open in less than fiveseconds and, in some cases, within three or four seconds.

The circuit breaker or motor protector of the present invention is particularly adapted for relatively small electric motors used on automotive vehicles for driving windshield wipers, window opening mechanisms and other devices. It may be used as a protector for the engines of electric toy trains and transformers. For these purposes and in other cases where space is limited the circuit breaker may have a width of from one-half to fiveeighths inch so that it takes up very little room.

The improved circuit breaker comprises a very few simple, inexpensive parts, which may be manufactured and assembled with very simple tools and with but a few operations. At the same time, a rugged and rigid construction is provided which will stand up under long use under the most severe operating conditions.

I claim:

1. A temperature-responsive circuit breaker, comprising a mounting including a metal plate having an elec trical terminal connection and a sheet of insulating maerial fixed to the underside of the metal plate, said metal plate having an opening, a fixed electrical contact secured to the sheet of insulating material and located in said opening in spaced relation to the metal plate, an

electrical terminal on the side of said sheet opposite said plate and electrically connected to said fixed contact, a snap-acting bimetallic thermostatic blade having highand low-expanding sides, said bimetallic blade comprising a substantially circular-shaped sheet bimetal body having a substantially symmetrical centrally-located integral tongue connected at one end to the body and separated therefrom by a U-shaped slot, means for securing and electrically connecting the tongue in fixed spaced relation to the metal plate, and an electrical contact fixed to the high-expanding side of the body of the bimetallic blade adjacent the other end of the tongue and normally engaging the fixed electrical contact.

2. A circuit breaker as claimed in claim 1, in which the bimetallic blade is substantially symmetrically concave on its high-expanding side and said tongue is straight and flat, whereby heating of the tongue by current flowing tberethrough causes the portion of the tongue extending to the body of the blade to move away from the metal plate and apply increasing pressure on the fixed contact up to the time when the blade snaps its contact away from the fixed contact.

3. In a temperature-responsive circuit breaker, a snapacting bimetallic thermostatic blade comprising a generally circular bimetallic sheet having a center, said sheet having two parallel straight edge portions disposed on opposite sides of said center and arranged symmetrically with respect thereto, said sheet having a U-shaped slot therein surrounding said center and having its side legs parallel to said straight edge portions, said U-shaped slot defining a tongue integral with said sheet and disposed in the center portion thereof, said sheet, except for said tongue, being of substantially spherical contour and being concave on its high expanding side, said tongue being fiat and straight and having its root end in the plane of the adjacent portion of said sheet, means to mount said tongue at said center, and a contact carried by said sheet adjacent the free end of said tongue.

4. In a temperature-responsive circuit breaker, a snapacting bimetallic thermostatic blade comprising a generally circular bimetallic sheet having a center, said sheet having a U-shaped slot therein surrounding said center and defining a tongue integral with said sheet and disposed in the center portion thereof, said sheet, except for said tongue, being of substantially spherical contour and being concave on its high-expanding side, said tongue being flat and straight and having its root end in the plane of the adjacent portion of said sheet, means to mount said tongue at said center, and a contact carried by said sheet adjacent the free end of said tongue and on the high expanding side of said sheet.

5. The circuit breaker of claim 4, in which the means to mount said tongue comprises a rivet extending through said center, and a deformable member is secured by said rivet and has a portion overlying the low expanding side of said sheet opposite said contact, said deformable member limiting the snapping movement of said sheet and being adapted to be deformed to effect adjustments in said movement.

References Cited in the file of this patent UNITED STATES PATENTS 2,182,048 Elmer Dec. 5, 1939 2,266,537 Elmer Dec. 16, 1941 2,361,162 Arnold Oct. 24, 1944 2,707,216 Farison Apr. 26, 1955 FOREIGN PATENTS 560,434 Great Britain Apr. 4, 1944 677,161 Great Britain Aug. 13, 1952 

